High-Latitude Electrodynamics During Magnetic Storms

Abstract:

During magnetic storms, energy is transferred from the solar wind to the ionosphere-thermosphere (IT) system. Energy input is dominated by electromagnetic power in the form of Poynting flux (PF) which can be dissipated as Joule heat in the ionosphere. Accurate specification of PF is central to any study of the response of the IT system to solar wind forcing. In our past work, we have reported on the discrepancies between observed PF for individual storm events and empirical models frequently used. In this paper, we summarize the results of our computed PF for 36 magnetic storms, during which 40 main phases were observed.

We subdivide our storm events into pre-storm quiet intervals, initial, main, and recovery phases. We use field and particle data from the Defense Meteorological Satellite Program (DMSP) satellites in our analysis. These are used in combination to (1) compute the electromagnetic power and (2) assign a location where the PF is measured, based on the precipitation particle characteristics observed simultaneously with the field measurements. From this characterization based on precipitating particles, we obtain a map of the source regions of PF for each of the phases of the storms under study, dividing PF locations into open and closed field line regions. Polar distributions show significant levels of PF at very high latitudes during all storm phases. There are distinct hemispheric asymmetries between spatial distributions and levels of PF. The locations of the open and closed field lines in this study, based on particle characteristics, show surprising mixing of latitudes and local times, presumably due to the dynamic nature of boundary motions during magnetic storms.